Gastric pH Distribution and Mixing of Soft and Rigid Food Particles in the Stomach using a Dual-Marker Technique

Mixing of a particle-laden material during peristaltic flow in the stomach has not been quantified in vivo. Gastric mixing plays a key role in the digestion process; it determines the availability of acid and enzymes to individual food particles and controls the length of time particles will spend in the antral region, where they are subjected to mechanical breakdown from antral contraction waves. Solid particle mixing has been quantified using a dual-indigestible marker technique (TiO₂ and Cr₂O₃) in soft (cooked brown and white rice) and rigid (raw and roasted almonds) particle meals fed to growing pigs. All meals consisted of two portions. Each portion was separately marked by one of the two indigestible markers, and the portions were sequentially fed to the pigs. At time periods ranging from 20 to 720 min after completion of the meal, ten intragastric chyme samples were taken from each pig to determine the marker concentration and pH value. Gastric pH was not homogeneous throughout the stomach and varied over time, with differences observed between soft and rigid meals (p?<?0.0001). The total percentage of each meal that was mixed was calculated using a statistically-based mixing index (M). White rice had the greatest amount of mixing, becoming 94 % mixed after 480 min of digestion compared to 72 % mixing for brown rice. Rigid particles underwent a slower mixing process and only arrived at 65 and 71 % mixing after 720 min for raw and roasted almonds, respectively. Meal composition plays a role in the overall meal mixing during gastric digestion.     

Digestion of Raw and Roasted Almonds in Simulated Gastric Environment

Knowledge of digestion kinetics of solid foods in human stomach, as affected by food processing methods, is critical in establishing processing conditions at the manufacturing stage to achieve desirable release of nutrients in the gastrointestinal tract. The objective of this study was to investigate how roasting affected disintegration and solid release properties of almond in simulated gastric environment. In vitro trials were performed for raw and roasted almonds by using static soaking method and a model stomach system. The changes in sample weight, dry mass, and moisture during the trials were determined. Both compression and penetration tests were used to investigate the texture of almonds with a focus on the influence of absorption of gastric juice. Light microscopy and transmission electronic microscopy were used to study the change in microstructure of the raw and roasted almonds after simulated digestion. The results suggested that the slow disintegration rate and the high amount of swelling of the almonds in the stomach may contribute to their high satiety property. Roasting significantly improved the disintegration rates of almonds and increased loss of solids during simulated digestion, which is well correlated with the decrease in the rigidity of almond samples after absorbing gastric juice. Microstructure of digested almonds showed breakage and breach of cell walls due to acid hydrolysis. Intercellular and intracellular channels formed in almonds during roasting are important for penetration of gastric juice that may facilitate an effective digestion.     

In vivo and in vitro starch digestion: are current in vitro techniques adequate?

The time evolution of the size distributions of (fully branched and debranched) starch molecules during in vivo and in vitro digestion was analyzed using size exclusion chromatography (SEC) and compared. In vivo digesta were collected from the small intestine of pigs fed with raw normal maize starch; in vitro digestion was carried out on the same diet fed to the pigs using a method simulating digestion in the mouth, stomach, and small intestine. A qualitative difference was observed between the in vitro and the in vivo digestion. The former showed a degradation of starch molecules to a more uniform size, whereas the in vivo digestion preserved the size distribution of native starch before producing a multimodal distribution, the heterogeneous nature of which current in vitro methods do not reproduce. The use of in vitro digestion to infer in vivo digestion patterns and, hence, potential nutrition benefits need to take account of this phenomenon.     

The response of gastric pH and motility to fasting and feeding in free swimming blacktip reef sharks, Carcharhinus melanopterus

In many fish and reptiles, gastric digestion is responsible for the complete breakdown of prey items into semi-liquid chyme. The responses of the stomach to feeding and to periods of fasting are, however, unknown for many lower vertebrates. We inserted data loggers into the stomachs of free-swimming captive adult blacktip reef sharks (Carcharhinus melanopterus) to quantify gastric pH, motility and temperature during fasting and following ingestion of food. Gastric acid secretion was continuous, even during long periods of fasting, with a mean pH of 1.66 ± 0.40 (± 1 SD) when the stomach was empty. Stomach contractions were greater following meals of mackerel than for those of squid. Gastric motility following feeding on mackerel, was positively influenced by ambient temperature, and followed a quadratic relationship with meal size, with maximum motility occurring after meals of 0.8-1.0% body weight. Diel changes in gastric motility were apparent, and were most likely caused by diel changes in ambient temperature. Gastric digestion in blacktip reef sharks is affected by both biotic and abiotic variables. We hypothesize that behavioral strategies adopted by sharks in the field may be an attempt to optimize digestion by selecting for appropriate environmental conditions.     

Particle morphology characterization and manipulation in biomass slurries and the effect on rheological properties and enzymatic conversion

An improved understanding of how particle size distribution relates to enzymatic hydrolysis performance and rheological properties could enable enhanced biochemical conversion of lignocellulosic feedstocks. Particle size distribution can change as a result of either physical or chemical manipulation of a biomass sample. In this study, we employed image processing techniques to measure slurry particle size distribution and validated the results by showing that they are comparable to those from laser diffraction and sieving. Particle size and chemical changes of biomass slurries were manipulated independently and the resulting yield stress and enzymatic digestibility of slurries with different size distributions were measured. Interestingly, reducing particle size by mechanical means from about 1 mm to 100 μm did not reduce the yield stress of the slurries over a broad range of concentrations or increase the digestibility of the biomass over the range of size reduction studied here. This is in stark contrast to the increase in digestibility and decrease in yield stress when particle size is reduced by dilute-acid pretreatment over similar size ranges.     

The role of cotyledon cell structure during in vitro digestion of starch in navy beans

Studies on the physico-chemical, microstructural characteristics and in vitro (under simulated gastric and small intestine conditions) starch digestibility of navy beans were carried out. The microstructure of raw and cooked beans observed through scanning electron microscopy (SEM) showed the presence of hexagonal or angular shaped cotyledon cells (50-100 μm size) containing starch granules with a size ranging between 10 and 50 μm. The extent of starch hydrolysis (%) after 120 min of in vitro gastro-intestinal digestion differed between whole navy beans (∼60%) and milled bean flour and bean starch (85-90%) after they were cooked under similar conditions. Starch hydrolysis (%) increased significantly when the cotyledon cells in the cooked whole navy beans were disrupted using high pressure treatment (French press). The storage of freshly cooked whole beans resulted in a lower (40-45%) starch hydrolysis whereas re-heating increased the same to 70-80% during in vitro small intestinal digestion. The SEM pictures of cooked navy bean digesta after different intervals of in vitro gastric and small intestinal digestion showed that the cotyledon cell structure is maintained well throughout the digestion period. However cotyledon cells appear shrunken and developed wrinkles during in vitro digestion. Particle size analysis of cooked bean paste taken before and after the in vitro gastro-intestinal digestion showed similar particle size distributions.     

Gastric emptying and the return of appetite in juvenile turbot, Scophthalmus maximus L., fed on artificial diets

Gastric emptying time in Scophthalmus maximus , when fed friable artificial pellets based on fishmeal, is composed of two phases:
(a) a delay time (t_d) during which the meal forms a bolus and which shortens with temperature, and
(b) an emptying phase (duration t_end ) which varies with meal size ( S ), body weight ( W ) and temperature (71 according to:
(where t _end is in h, S is in g, W is in g and T is °C). During the emptying phase, stomach contents decrease curvilinearly according to:
(where S_t , & S_o is in g and t is in h) in which the instantaneous digestion rate, K , varies with fish weight and temperature as:
Food pellets were prepared which remained separate and did not form a bolus in the stomach; K increased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets, K decreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs at c. 85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two-thirds of the previous rate since stomach fullness, and hence digestion rate (g h⁻¹), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g⁻¹ increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy-rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and frequency.     

The effects of temperature and meal size on the rate of gastric evacuation in perch (Perca fluviatilis) fed on fish larvae

SUMMARY. The rate of gastric evacuation in perch (Perca fluviatilis) (89–170 mm length) fed on fish larvae was studied at temperatures between 12.0 and 21.7°C. Gastric evacuation rates were usually described by an exponential function. The instantaneous rate of gastric evacuation ( R ) was constant for a large number of different meal sizes. At higher food rations, a lag phase in digestion was found during the first part of digestion, and this ration size was smaller for smaller perch (89–110 mm) than for bigger perch (120–170 mm). Below these larger meal sizes, gastric evacuation was similar for the different size classes studied. The relation between R and temperature was described by an exponential function. The effects of meal size, number of food items, fish size and temperature on the rate of gastric evacuation are discussed.     

On the kinematics and efficiency of advective mixing during gastric digestion – A numerical analysis

The mixing performance of gastric contents during digestion is expected to have a major role on the rate and final bioavailability of nutrients within the body. The aim of this study was to characterize the ability of the human stomach to advect gastric contents with different rheological properties. The flow behavior of two Newtonian fluids (10⁻³ Pa s, 1 Pa s) and a pseudoplastic solution (K=0.223 Pa s^0.59) during gastric digestion were numerically characterized within a simplified 3D model of the stomach geometry and motility during the process (ANSYS-FLUENT). The advective performances of each of these gastric flows were determined by analyzing the spatial distribution and temporal history of their stretching abilities (Lagrangian analysis). Results illustrate the limited influence that large retropulsive and vortex structures have on the overall dynamics of gastric flows. Even within the distal region, more than 50% of the flow experienced velocity and shear values lower than 10% of their respective maximums. While chaotic, gastric advection was always relatively poor (with Lyapunov exponents an order of magnitude lower than those of a laminar stirred tank). Contrary to expectations, gastric rheology had only a minor role on the advective properties of the flow (particularly within the distal region). As viscosity increased above 1 St, the role of fluid viscosity became largely negligible. By characterizing the fluid dynamic and mixing conditions that develop during digestion, this work will inform the design of novel in vitro systems of enhanced biomechanical performance and facilitate a more accurate diagnosis of gastric digestion processes.     

Acidic digestion in a teleost: postprandial and circadian pattern of gastric pH, pepsin activity, and pepsinogen and proton pump mRNAs expression

Two different modes for regulation of stomach acid secretion have been described in vertebrates. Some species exhibit a continuous acid secretion maintaining a low gastric pH during fasting. Others, as some teleosts, maintain a neutral gastric pH during fasting while the hydrochloric acid is released only after the ingestion of a meal. Those different patterns seem to be closely related to specific feeding habits. However, our recent observations suggest that this acidification pattern could be modified by changes in daily feeding frequency and time schedule. The aim of this study was to advance in understanding the regulation mechanisms of stomach digestion and pattern of acid secretion in teleost fish. We have examined the postprandial pattern of gastric pH, pepsin activity, and mRNA expression for pepsinogen and proton pump in white seabream juveniles maintained under a light/dark 12/12 hours cycle and receiving only one morning meal. The pepsin activity was analyzed according to the standard protocol buffering at pH 2 and using the actual pH measured in the stomach. The results show how the enzyme precursor is permanently available while the hydrochloric acid, which activates the zymogen fraction, is secreted just after the ingestion of food. Results also reveal that analytical protocol at pH 2 notably overestimates true pepsin activity in fish stomach. The expression of the mRNA encoding pepsinogen and proton pump exhibited almost parallel patterns, with notable increases during the darkness period and sharp decreases just before the morning meal. These results indicate that white seabream uses the resting hours for recovering the mRNA stock that will be quickly used during the feeding process. Our data clearly shows that both daily illumination pattern and feeding time are involved at different level in the regulation of the secretion of digestive juices.     

Effect of feeding frequency on the daily rhythms of acidic digestion in a teleost fish (gilthead seabream)

Gilthead seabream is a fish species of great importance in Mediterranean aquaculture, attracting many studies on nutrition and chronobiology, although nothing is known about the effect of feeding frequency on the daily rhythms of the gastric digestion process. In this article, we investigated daily rhythms in stomach fullness, gastric and intestine pH, as well as pepsin activity and expression of pepsinogen and proton pump in juvenile fish under three different feeding protocols: (A) one daily meal at 9:00, (B) two daily meals at 9:00 and 17:00 and (C) continuous feeding during the daytime. The results revealed that feeding protocol affected significantly the rhythm of gastric pH and the pepsin activity pattern. The gastric pH exhibited significant daily rhythms in the three cases with the acrophase located at night in the regimes A and B and during daytime, in the regime C. In the regimes A and B, the pepsin activity peaked few hours after the meals, although the afternoon meal in B produced a higher peak. In the regime C, the peak occurred in the middle of the feeding period. Lowest total pepsin activity was observed in regime A, and the highest activity with the regime C. In contrast, the pepsinogen gene expression remained low along the daily cycle, with an expression peak just before or after the morning meal in regimes A and C, respectively. The proton pump gene expression was also practically constant with a peak right after the morning meal in the regime C. On the other hand, intestinal pH showed a postprandial increase after the first morning meal in all the three treatments, recovering the resting values in the dark period. Two meals and continuous feeding allowed a better and prolonged gastric digestion and consequently the juveniles exhibited better growth with the same daily ration of food. In short, while the gastric digestion pattern is mainly driven by pH changes induced by the time of food ingestion, the regulation of the intestinal digestion seems to be more independent of the feeding protocol.     

Postprocessing In Vitro Digestion Challenge To Evaluate Survival of Escherichia coli O157:H7 in Fermented Dry Sausages

Fermented dry sausages, inoculated with Escherichia coli O157:H7 during batter preparation, were submitted to an in vitro digestion challenge to evaluate the extent to which passage through the human gastrointestinal tract could inactivate the pathogenic cells, previously stressed by the manufacturing process. The numbers of surviving E. coli O157:H7 cells remained constant after a 1-min exposure of the finely chopped sausage to synthetic saliva or during the following 120-min exposure to synthetic gastric juice at an initial pH of 2.0. However, significant (P ≤ 0.05) growth of the pathogen (1.03 to 2.16 log₁₀ CFU/g) was observed in a subsequent 250-min exposure to a synthetic pancreatic juice at pH 8.0. In a different set of experiments, fractions from the gastric suspension were transferred into the synthetic pancreatic juice at 30-min intervals to mimic the dynamics of gastric emptying. Concurrently, the pH of the remaining gastric fluid was reduced to 3.0, 2.5, and 2.0 to simulate the gradual reacidification of the stomach contents after the initial buffering effect resulting from meal ingestion. Under these new conditions, pathogen growth during pancreatic challenge was observed for the first few fractions released from the stomach (90 min of exposure [pH 2.5]), but growth was no longer possible in the fractions submitted to the most severe gastric challenge (120 min of exposure [pH < 2.2]).     

Quantification of gastric secretions in the wild whiting fed on natural prey in captivity

Quantification of gastric acid and enzyme pepsin in the gastric phase of digestion in wild whiting (Merlangius merlangus L.) were elucidated in the present study. The results showed that after ingestion of a meal, first pepsin and, more slowly, gastric acid (hydrochloric acid) was secreted into the gastric lumen to peak at 2–4 h (49.4–53.8 mEq wt acid × 10³; 652–813 μg pepsin ml Eq min^?1). Fish size had a significant influence on the amount of gastric acid and pepsin secreted; digestive power increased α W^0.67, as predicted by the ‘physiological’ model. However, the predicted effects of meal size [stimulus, distension volume (DV)] were not clear. Instead, the stomach distension model for flatfish from a previous worker showed that muscular contractions (mixing mechanism) were related to DV^0.33 and found to partially support the physiological model in the present study.     

Postprandial responses in the African rhombig egg eater (Dasypeltis scabra)

The African rhombic egg eater (Dasypeltis scabra) is a colubrid snake feeding exclusively on bird eggs. Frequency of feeding is governed by the seasonal availability of bird eggs; i.e., long fasting intervals change with relatively short periods when plenty of food is available. Intermittent feeding snakes show a remarkable postprandial increase of metabolic rate and digestive organ size. The postprandial increase in metabolic rate (specific dynamic action, SDA) in snakes is affected by meal size, temperature, and meal composition. A major portion of SDA in snakes is allocated to gastric function and the breakdown of the meal. We hypothesize that SDA in egg eaters is lower than in other snake species, because egg eaters feed on “liquid” food that does not require enzymatic breakdown in the stomach. We also hypothesized that other components of the postprandial response of egg eaters (e.g., size changes of the intestine and the liver) do not differ from other snakes. The standard metabolic rate and metabolic response to feeding were measured using closed-chamber respirometry. Size changes of small intestine and liver were measured using high-resolution transcutaneous ultrasonography. Standard metabolic rates of fasting egg eaters were in the same range of mass specific values as known from other snakes. Within 24 h after feeding, oxygen consumption doubled and peaked at 2 days after feeding. At the same time, the size of the small intestine and the cross-sectional diameter of the liver increased. Within 2 days after feeding, the size of the mucosal epithelium doubled its thickness. Liver size increased significantly within 24 h reaching maximum size 2–4 days after feeding. The size of both organs returned to fasting values within 7–10 days after feeding. The postprandial response of African rhombic egg eaters shows the same pattern and dynamics as known from other snake species. However, the factorial increase of metabolic rate during SDA is the lowest reported for any snake. A comparison with literature data supports the idea that SDA is mainly determined by gastric function and that it is low in egg eaters because they do not have to break down solid meals in the stomach as other snake species do.     

Effects of meal size,meal type,body temperature,and body size on the specific dynamic action of the marine toad,Bufo marinus

Specific dynamic action (SDA), the accumulated energy expended on all physiological processes associated with meal digestion, is strongly influenced by features of both the meal and the organism. We assessed the effects of meal size, meal type, body temperature, and body size on the postprandial metabolic response and calculated SDA of the marine toad, Bufo marinus. Peak postprandial rates of O(2) consumption (.V(O2)) and CO(2) production (.V(CO2)) and SDA increased with meal size (5%-20% of body mass). Postprandial metabolism was impacted by meal type; the digestion of hard-bodied superworms (Zophobas larva) and crickets was more costly than the digestion of soft-bodied earthworms and juvenile rats. An increase in body temperature (from 20 degrees to 35 degrees C) altered the postprandial metabolic profile, decreasing its duration and increasing its magnitude, but did not effect SDA, with the cost of meal digestion remaining constant across body temperatures. Allometric mass exponents were 0.69 for standard metabolic rate, 0.85 for peak postprandial .V(O2), and 1.02 for SDA; therefore, the factorial scope of peak postprandial .V(O2) increased with body mass. The mass of nutritive organs (stomach, liver, intestines, and kidneys) accounted for 38% and 20% of the variation in peak postprandial .V(O2) and SDA, respectively. Toads forced to exercise experienced 25-fold increases in .V(O2) much greater than the 5.5-fold increase experience during digestion. Controlling for meal size, meal type, and body temperature, the specific dynamic responses of B. marinus are similar to those of the congeneric Bufo alvarius, Bufo boreas, Bufo terrestris, and Bufo woodhouseii.     

Formation,Stability and In Vitro Digestion of β-carotene in Oil-in-Water Milk Fat Globule Membrane Protein Emulsions

The formation, stability and in vitro digestion of milk fat globule membrane (MFGM) proteins stabilized emulsions with 0.2 wt% β-carotene were investigated. The average particle size of β-carotene emulsions stabilized with various MFGM proteins levels (1%, 2%, 3%, 4%, 5% wt%) decreased with the increase of MFGM proteins levels. When MFGM proteins concentration in emulsions is above 2%, the average particle size of β-carotene emulsions is below 1.0 μm. A quite stable emulsion was formed at pH 6.0 and 7.0, but particle size increased with decrease in acidity of the β-carotene emulsion. β-carotene emulsions stabilized with MFGM proteins were stable with a certain salt concentrations (0–500 mMNaCl). β-carotene emulsions were quite stable to aggregation of the particles at elevated temperature and time (85 °C for 90 min). At the same time, β-carotene emulsions were stable against degradation under heat treatment conditions. In vitro digestion of β-carotene emulsion showed the mean particle size of β-carotene emulsions stabilized with MFGM proteins in the simulated stomach conditions and intestinal conditions is larger than that of initial emulsions and simulated mouth conditions. Confocal laser scanning microscopy of β-carotene MFGM proteins emulsions also showed the corresponding results to different vitro digestion model. There was a rapid release of free fatty acid (FFA) during the first 10 min and after this period, an almost constant 70% digestion extent was reached. Approximately 80% of β-carotene was released within 2 h of incubation under the simulated intestinal fluid. These results showed that MFGM protein can be used as a good emulsifier in emulsion stabilization, β-carotene rapid release as well as lipophilic bioactive compounds delivery.     

Influence of Particle Size and Concentration on Rheological Behaviour of Reconstituted Apple Purees

This work investigates the impact of structural parameters on the rheological behaviour of apple purees. Reconstructed apple purees from 0 g/100 g up to 2.32 g/100 g of insoluble solids content and varying in particle size were prepared. Three different particle size distributions were obtained by mechanical treatment only, to modify both size and morphology of the particles without modifying the intrinsic rigidity of the cell walls. Rheological measurements showed that the insoluble solids content have a first order effect on the rheological behaviour of the suspensions: three concentrations domains were observed in both dynamic and flow measurements. A model is proposed for each domain. The existence of a weak network between particles is clearly shown over a critical concentration of insoluble solids (cell walls) depending on particle size distribution (semi-diluted domain). In a concentrated domain, particles are on close packing conditions and their apparent volume begin to shrink. Particle size and shape also play an important role on the rheological behaviour of reconstructed apple puree. Due to their irregular shape, cell clusters clog the medium at lower concentration compared to individual cells.     

Particle size distribution of rice flour affecting the starch enzymatic hydrolysis and hydration properties

Rice flour is becoming very attractive as raw material, but there is lack of information about the influence of particle size on its functional properties and starch digestibility. This study evaluates the degree of dependence of the rice flour functional properties, mainly derived from starch behavior, with the particle size distribution. Hydration properties of flours and gels and starch enzymatic hydrolysis of individual fractions were assessed. Particle size heterogeneity on rice flour significantly affected functional properties and starch features, at room temperature and also after gelatinization; and the extent of that effect was grain type dependent. Particle size heterogeneity on rice flour induces different pattern in starch enzymatic hydrolysis, with the long grain having slower hydrolysis as indicated the rate constant (k). No correlation between starch digestibility and hydration properties or the protein content was observed. It seems that in intact granules interactions with other grain components must be taken into account. Overall, particle size fractionation of rice flour might be advisable for selecting specific physico-chemical properties.